Percentage Mental Math in Real Life Application

Let’s delve into some common types of Percentage calculations and then let’s see its use in real life

1. What is x% of y?
Formula: $\frac{x}{100}$ $\times$ y
Example: What is 30% of 250?
Solution: $\frac{30}{100}$ $\times$ 250 = 75

    2. x is what % of y?
    Formula: $\frac{x}{y}$ $\times$ 100
    Example: 50 is what % of 200
    Solution: $\frac{50}{200}$ $\times$ 100 = 25%

    3. x is y% of what number?
    Formula: $\frac{x}{(y/100)}$
    Example: 50 is 20% of what number?
    Solution: $\frac{50}{0.2}$ = 250

    Real-Life Applications

    Here we connect percentages with everyday scenarios for practical learning.

    ScenarioFormulaExampleCalculation
    DiscountsFinal Price = Original $\times$ 1- $\frac{Discount％}{100}$ You go to a newly opened shop and you see they are offering 20% discount on brand new shoes costing $500. How much are the shoes really going to cost you after discount? Don’t ask the shopkeeper, just calculate!500 $\times$ 0.8 = 400
    Tax AdditionFinal Price = Original $\times$ $\frac{Tax％}{100}$You see nice buffet ad at a restaurant but it cost you 100$ excluding the tax. How much extra you need to pay extra for the tax? Don’t ask the restaurant, let’s just calculate in seconds!100 $\times$ 0.18 = 18
    Simple Interest$\frac{P \times R \times T}{100}$ Your Bank for the years had been giving you annual interest of 5% on $1,000. How much is that money actually earning? Let’s not go into bank statements to find out. We can do mental math!1000 $\times$ 0.05 = 50

    So next time you come across tax, discount or bank interest calculation, use this shortcuts to calculate!

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